Candles may not be the first thing that come to mind when you think of plastic, but most candles are now made of paraffin wax (which is made from petroleum), and the synthetic fragrances which many contain aren't so good for you.
An awesome alternative is beeswax. Beeswax candles are not only a more natural option, they may actually purify the air. You can buy them (I got this one on Etsy), or make your own. When the candle has reached the end of its life, the beeswax can be composted.
If you aren't familiar with Plastic Free July, take a look at this post. Basically, it's a month-long challenge to reduce the amount of disposable plastic you use. It's a great starting point if you just want to give cutting out disposable plastic a try.
My first Plastic Free July was in 2013(!), and this month I'd like to highlight some of the things I do to reduce my plastic use, and some struggles. Many things are part of my routine at this point (buying in bulk, refusing plastic silverware, etc.), but I am not perfect, and I always find this challenge to be a good time to refocus and look at what trash I am actually producing.